Thin Film Capacitor and Manufacturing Method Therefor

ABSTRACT

A thin film capacitor including a substrate, a capacitor portion having an upper conductor, a lower conductor, and a dielectric thin film, and a resin protective layer for protecting the capacitor portion. A barrier layer is interposed between the capacitor portion and the resin protective layer. The barrier layer includes a crystalline dielectric barrier layer formed in contact with the capacitor portion and having the same composition system as the dielectric thin film, and an amorphous inorganic barrier layer formed on the surface of the crystalline dielectric barrier layer and composed of silicon nitride having non-conductivity. The inorganic barrier layer prevents deterioration in the properties of the dielectric thin film by blocking diffusion of the constituent elements of the inorganic barrier layer toward the capacitor portion.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of International ApplicationNo. PCT/JP2006/302254, filed Feb. 9, 2006, which claims priority toJapanese Patent Application No. JP2005-130171, filed Apr. 27, 2005, theentire contents of each of these applications being incorporated hereinby reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to a thin film capacitor used fordecoupling an integrated circuit and a manufacturing method therefor.

BACKGROUND OF THE INVENTION

Decoupling capacitors have been used with increases in processing speedof integrated circuits. Decoupling capacitors are required to have lowESL (Equivalent Series Inductance). As a decoupling capacitor satisfyingthis requirement, there has been known a thin film capacitor having acapacitor portion which is formed on a Si substrate by a thin filmtechnique such as a sputtering or sol-gel method.

Such a thin film capacitor is coated with a protective layer composed ofa resin material for mechanically reinforcing a capacitor portion. Forexample, Patent Document 1 has proposed a thin film capacitor includinga capacitor having a dielectric layer composed of a metal oxide and aprotective insulating layer composed of a resin material, a barrierlayer composed of a nonconductive inorganic material being providedbetween the capacitor and the protective insulating layer.

As shown in FIG. 4, the thin film capacitor of Patent Document 1includes a Si substrate 101, a capacitor 109 having a lower electrodelayer 102, a dielectric layer 103 composed of barium strontium titanate(referred to as “BST” hereinafter), and an upper electrode layer 104,which are formed in order on the Si substrate 101, a barrier layer 105formed to cover the capacitor 109, a protective insulating layer 106formed on the barrier layer 105 and composed of a resin material,electrode pads 107, and bumps 108.

The barrier layer 105 is provided for preventing the dielectric layer103 composed of BST from being reduced with moisture released from theresin material contained in the protective insulation layer 106.Examples of a material preferably used for forming the barrier layer 105include amorphous materials, such as silicon nitride (Si₃N₄), aluminumoxide (Al₂O₃), silicon oxide (SiO₂), and amorphous BST.

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 2004-214589

However, in the thin film capacitor described in Patent Document 1, thebarrier layer 105 composed of an amorphous nitride such as amorphoussilicon nitride may diffuse nitrogen atoms toward the dielectric layer103 through the upper electrode layer 104 to change the composition ofBST, thereby failing to obtain desired electric properties.

Also, the barrier layer 105 composed of amorphous aluminum oxide oramorphous silicon oxide may diffuse aluminum or silicon toward thedielectric layer 103. Therefore, such a material is undesirable.

Further, heat treatment is required for thermally curing the resinconstituting the protective insulating layer 106. However, the barrierlayer composed of an amorphous oxide such as amorphous BST causes theproblem that the amorphous oxide takes oxygen away from the dielectriclayer 103 through the upper electrode layer 104. Consequently, thecomposition of the dielectric layer 103 is changed, thereby failing toachieve desired electric properties. This is because an amorphous oxideis generally assumed to have the oxygen content smaller than thestoichiometric composition. Thus, oxygen is taken away from thedielectric layer 103 of crystalline BST having a higher oxygen contentthan that of the amorphous oxide. The barrier layer 105 composed ofcrystalline BST, not amorphous BST, does not cause the problem asdescribed above. However, as described in Patent Document 1, the barrierlayer 105 composed of crystalline BST can produce substantially nobarrier effect.

After all, in the invention described in Patent Document 1, theproperties of the dielectric layer 103 may be degraded by providing thebarrier layer 105.

SUMMARY OF THE INVENTION

The present invention has been achieved in consideration of theabove-mentioned situation. The object of the present invention is toprovide a thin film capacitor capable of preventing deterioration ofproperties even when a layer with a barrier function is provided betweena capacitor portion and a resin protective layer (protective insulationlayer), and a manufacturing method therefor.

In order to achieve the object, a thin film capacitor according to thepresent invention includes a substrate, a capacitor portion formed onthe substrate and including a plurality of conductor layers and adielectric thin film, and a resin protective layer for protecting thecapacitor portion, wherein a barrier layer is interposed between thecapacitor portion and the resin protective layer, and the barrier layerincludes a crystalline dielectric barrier layer which is formed incontact with the capacitor portion and which has the same compositionsystem as the dielectric thin film and a non-conductive amorphousinorganic barrier layer formed on the surface of the dielectric barrierlayer.

In the present invention, the term “the same composition system” meansthat the constituent elements are the same and includes the idea thatthe molar content ratios of the constituent elements are different. Forexample, when the dielectric thin film and the barrier layer are formedusing (Ba, Sr)TiO₃ (BST), the dielectric thin film and the dielectricbarrier layer have the same composition system even when the molarcontent ratios of Ba and Sr are different.

In the thin film capacitor of the present invention, the inorganicbarrier layer preferably contains at least one material selected fromsilicon nitride, aluminum oxide, and silicon oxide. Silicon nitride isparticularly preferred from the viewpoint of improvement in moistureresistance because the moisture resistance can be obtained with arelatively small film thickness.

In the present invention, “silicon nitride” is preferably Si₃N₄ havingthe stoichiometric composition in which the molar ratio of silicon tonitrogen is 3:4, but the silicon nitride is not necessarily limited tothis. The silicon nitride may have a silicon/nitrogen molar ratiodifferent from that of the stoichiometric composition as long as it hasnon-conductivity and moisture resistance. In this sense, in thespecification, the silicon nitride may be denoted by SiN_(x).

In the thin film capacitor of the present invention, the crystallinedielectric barrier layer preferably has the same composition as thedielectric thin film.

Further, in the thin film capacitor of the present invention, anadhesive layer composed of a material with the same composition systemas the dielectric thin film is provided between the substrate and thecapacitor portion.

The adhesive layer preferably has the same composition system as thedielectric thin film.

A method of manufacturing a dielectric thin film capacitor according tothe present invention includes a step of applying a first dielectric rawmaterial solution containing an organic metal compound on a substrateand heating the solution to form an adhesive layer, a step ofalternately depositing, on the adhesive layer, a conductor layer and adielectric thin film formed by applying a second dielectric raw materialsolution with the same composition system as that of the first electricraw material solution to form a capacitor portion, a step of applying,on the capacitor portion, a third dielectric raw material solution withthe same composition system as that of the first or second electric rawmaterial solution and heating the solution to form a crystallinedielectric barrier layer, a step of performing a heat treatment at atemperature of 750° C. or more in an oxygen atmosphere, a step offorming a non-conductive amorphous inorganic barrier layer on thedielectric barrier layer, and a step of forming a resin protective layeron the inorganic barrier layer.

A thin film capacitor of the present invention includes a substrate, acapacitor portion formed on the substrate and including a plurality ofconductor layers and dielectric thin film, a resin protective layer forprotecting the capacitor portion, and a barrier layer interposed betweenthe capacitor portion and the resin protective layer, the barrier layerincluding a crystalline dielectric barrier layer formed in contact withthe capacitor portion and having the same composition system as thedielectric thin film and a non-conductive amorphous inorganic barrierlayer (silicon nitride, aluminum oxide, or silicon oxide) formed on thesurface of the dielectric barrier layer. Therefore, the moistureresistance of the capacitor portion can be improved by the inorganicbarrier layer and diffusion of the constituent components of theinorganic barrier layer toward the capacitor portion can be prevented bythe crystalline dielectric barrier layer, thereby preventing theinfluence of the inorganic barrier layer on the properties of thedielectric thin film. Since the dielectric barrier layer has the samecomposition system as that of the dielectric thin film, the propertiesof the dielectric thin film are not degraded even when the components ofthe dielectric barrier layer diffuse toward the capacitor portion.

In particular, when the dielectric barrier layer has the samecomposition system as that of the dielectric thin film, these can beformed through the same process using the same raw materials, therebydecreasing the manufacturing cost.

Further, an adhesive layer composed of a material with the samecomposition system as the dielectric thin film is provided between thesubstrate and the capacitor portion, so that the adhesion between thesubstrate and the capacitor portion can be improved. In particular, theconductor layers composed of Pt have weak adhesion to Si generally usedfor the substrate. Thus, the adhesion between the substrate and thecapacitor portion can be improved by providing the adhesive layerbetween the substrate and the capacitor portion. In addition, theadhesive layer has the same composition system as the dielectric thinfilm, and thus the properties of the dielectric thin film are notdegraded even when the component of the dielectric barrier layerdiffuses toward the capacitor portion.

In particular, the adhesive layer having the same composition system asthat of the dielectric thin film can be formed through the same processusing the same raw materials as those of the dielectric thin film.Therefore, the manufacturing cost is decreased.

A method of manufacturing a dielectric thin film capacitor according tothe present invention includes a step of applying a first dielectric rawmaterial solution containing an organic metal compound on a substrateand heating the solution to form an adhesive layer, a step ofalternately depositing, on the adhesive layer, a conductor layer and adielectric thin film formed by applying a second dielectric raw materialsolution with the same composition system as that of the first electricraw material solution to form a capacitor portion, a step of applying,on the capacitor portion, a third dielectric raw material solution withthe same composition system as that of the first or second electric rawmaterial solution and heating the solution to form a crystallinedielectric barrier layer, a step of performing a heat treatment at atemperature of 750° C. or more in an oxygen atmosphere, a step offorming a non-conductive amorphous inorganic barrier layer on thedielectric barrier layer, and a step of forming a resin protective layeron the inorganic barrier layer. Thus, it is possible to manufacture athin film capacitor having the above constitution without deterioratingthe properties of the dielectric thin film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a thin film capacitor according to anembodiment of the present invention.

FIG. 2 is a sectional view (½) showing steps for manufacturing a thinfilm capacitor according to an embodiment of the present invention.

FIG. 3 is a sectional view ( 2/2) showing steps for manufacturing a thinfilm capacitor according to an embodiment of the present invention.

FIG. 4 is a sectional view showing an example of conventional thin filmcapacitors.

REFERENCE NUMERALS

-   -   10 substrate    -   20 adhesive layer    -   30 capacitor portion    -   31 lower conductor (conductor layer)    -   32 dielectric thin film    -   33 upper conductor (conductor layer)    -   40 barrier layer    -   41 dielectric barrier layer    -   42 inorganic barrier layer    -   50 resin protective layer

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be described with referenceto the drawings.

FIG. 1 is a sectional view showing a thin film capacitor according to anembodiment of the present invention.

The thin film capacitor includes a substrate 10, an adhesive layer 20, acapacitor portion 30 including a lower conductor 31, a dielectric thinfilm 32, and an upper conductor 33, which are formed in order on theadhesive layer 20, a barrier layer 40 having a two-layer structureincluding a dielectric barrier layer 41 and an inorganic barrier layer42 which are formed in order to cover the capacitor portion 30, a resinprotective layer 50 formed to cover the barrier layer 40, electrode pads61 electrically connected to one of the lower conductor 31 and the upperconductor 33 and drawn out to the top surface through the resinprotective layer 50, and bumps 62 formed on the respective electrodepads 61.

The substrate 10 includes a Si layer 11 and a SiO₂ film 12 formed on thesurface of the Si layer 11.

The adhesive layer 20, the dielectric thin film 32, and the dielectricbarrier layer 41 are composed of crystalline BST and, in thisembodiment, have the same composition, i.e., the same molar contentratio of each constituent element of BST. The lower conductor 31 and theupper conductor 33 are composed of Pt. The inorganic barrier layer 42 isprovided for improving moisture resistance and, in this embodiment,composed of amorphous silicon nitride (SiN_(x)). The resin protectivelayer 50 is formed by thermally curing photosensitive BCB(benzocyclobutene).

In this embodiment, the inorganic barrier layer 42 is provided incontact with the lower surface of the resin protective layer 50.Therefore, the barrier effect of the inorganic barrier layer 42 canprevent the dielectric thin film 32, i.e., BST, from being reduced withmoisture released from the BCB resin of the resin protective layer 50,and can improve the moisture resistance of the capacitor portion 30. Inaddition, since the crystalline dielectric barrier layer 41 isinterposed between the inorganic barrier layer 42 and the capacitorportion 30, it is possible to inhibit diffusion of the inorganic barrierlayer 42, i.e., amorphous silicon nitride (SiN_(x)), toward thecapacitor portion 30. Therefore, the dielectric thin film 32 is notinfluenced by the inorganic barrier layer 42, and deterioration of theproperties of the thin film capacitor can be prevented.

Further, the adhesive layer 20, the dielectric thin film 32, and thedielectric barrier layer 41 have the same composition and can thus beformed through the same process using the same raw material. Therefore,the manufacturing cost can be decreased.

Next, the method for manufacturing the thin film capacitor will bedescribed.

First, as shown in FIG. 2( a), the substrate 10 including the Si layer11 and the SiO₂ layer 12 formed on the surface of the Si layer 11 isprepared. The adhesive layer 20 composed of crystalline BST having athickness of 100 nm is formed on the substrate 10. Then, the lowerconductor 31 composed of Pt having a thickness of 200 nm, the dielectricthin film 32 composed of crystalline BST having a thickness of 100 nm,and the upper conductor 33 composed of Pt having a thickness of 200 nmare deposited in order on the adhesive layer 20 to form the capacitorportion 30.

Specifically, the adhesive layer 20 can be formed by a MOD (MetalOrganic Decomposition) method. Namely, a dielectric raw materialsolution (first dielectric raw material solution) containing anorganometallic compound prepared at a molar ratio of Ba:Sr:Ti=7:3:10 isapplied on the substrate 10 by spin coating, dried, and thenheat-treated in an oxygen atmosphere, for example, at 650° C. for 30minutes to form the adhesive layer 20. The lower conductor 31 and theupper conductor 33 can be formed by, for example, a sputtering method.

The dielectric thin film 32 can be formed by applying a dielectric rawmaterial solution (second dielectric raw material solution) having thesame composition as that used for the adhesive layer 20 by spin coating,drying, and then heat treatment in an oxygen atmosphere, for example, at650° C. for 30 minutes. In this step, the dielectric thin film 32 neednot be sufficiently crystallized.

Next, a photoresist is applied on the upper conductor 33, followed byexposure, development, and ion milling to pattern the upper conductor 33as shown in FIG. 2 (b).

Next, a dielectric raw material solution (third dielectric raw materialsolution) having the same composition as that used for the adhesivelayer 20 and the dielectric thin film 32 is applied by spin coating,dried, and then heat-treated in an oxygen atmosphere, for example, at650° C. for 30 minutes to form the dielectric barrier layer 41 having athickness of 100 nm as shown in FIG. 2( c). Although, in this step, thedielectric barrier layer 41 need not be sufficiently crystallized, thedielectric barrier layer 41 is required to be sufficiently crystallizeduntil the resin protective layer 50 shown in FIG. 1 is thermally cured.

Next, heat treatment is performed in an oxygen atmosphere at atemperature of 750° C. or more, for example, 850° C., for 30 minutes toincrease the crystallinity of the dielectric thin film 32 and improvethe dielectric constant. The heat treatment also can increase thecrystallinity of the adhesive layer 20 and the dielectric barrier layer41.

Next, a photoresist is applied on the dielectric barrier layer 41,followed by exposure, development, and wet etching to partially removethe dielectric barrier layer 41 and the dielectric thin film 32 as shownin FIG. 2( d) and partially expose the upper conductor 33 and the lowerconductor 31.

Further, a photoresist is applied, followed by exposure, development,and ion milling to partially remove the adhesive layer 20, the lowerconductor 31, the dielectric barrier layer 32, the upper conductor 33,and the dielectric barrier layer 41 near the peripheral edge of thesubstrate 10 as shown in FIG. 3( e).

Next, silicon nitride (SiN_(x)) is deposited to a thickness of 500 nm bysputtering. Then, a photoresist is applied, followed by exposure,development, and reactive ion etching to partially expose the upperconductor 33 and the lower conductor 31 as shown in FIG. 3( f). As aresult, apertures 70 a and 70 b are provided, and the inorganic barrierlayer 42 composed of silicon nitride (SiN_(x)) is formed.

Next, photosensitive BCB resin is applied, followed by exposure,development, and then thermal curing at, for example, 250° C. to formthe resin protective layer 50 as shown in FIG. 3( g).

Next, a Ti film having a thickness of 50 nm, a Ni film having athickness of 2,000 nm, and an Au film having a thickness of 100 nm aredeposited in order by sputtering to form the electrode pads 61 as showin FIG. 3( h). Next, Sn—Ag—Cu solder paste is printed on the electrodepads 61, followed by reflowing at a temperature of, for example, 240°C., to form the bumps 62. As a result, the thin film capacitor ismanufactured.

In the method for manufacture the thin film capacitor, reduction of thedielectric thin film 32 can be prevented by the resin protective layer50, and the moisture resistance of the capacitor portion 30 can beimproved. In addition, the crystalline dielectric barrier layer 41 isformed between the inorganic barrier layer 42 and the capacitor portion30, and thus nitrogen atoms of silicon nitride constituting theinorganic barrier layer 42 can be prevented from diffusing toward thedielectric thin film 32 in thermal curing of the resin protective layer50 and heat treatment reflowing. Therefore, it is possible to preventdeterioration in properties of the dielectric thin film 32.

The present invention is not limited to the above-described embodiment,and various modifications may be made within the scope and gist thereof.For example, the substrate 10 is required for forming the capacitorportion 30 (the lower conductor 31, the upper conductor 33, and thedielectric thin film 32), but when the mechanical strength of thecapacitor 30 can be secured, the substrate 10 may be omitted by anappropriate method because the substrate 10 is irrelevant to theelectric operation of the thin film capacitor.

Although, in the above-described embodiment, the adhesive layer 20, thedielectric thin film 32, and the dielectric barrier layer 41 arecomposed of crystalline BST having the same composition, the propertiesof the dielectric thin film 32 are not deteriorated because the samecomposition system is used. Therefore, the molar content ratio of eachconstituent element of BST may be different in these layers.

The material of the dielectric thin film is not particularly limited aslong as it is a metal oxide having a perovskite structure which canexhibit a high dielectric constant. As well as BST, barium titanate,strontium titanate, lead titanate, and lead titanate zirconate can beused as the material of the dielectric thin film. Other examples includematerials having a bismuth layered structure, such as bismuth titanate,bismuth strontium tantalate, bismuth barium tantalate, bismuth strontiumniobate, and bismuth barium niobate; and materials having a tungstenbronze structure, such as barium strontium niobate.

The method for forming the dielectric thin film 32 is not limited to theMOD method, and, for example, a sputtering method may be used. When thedielectric thin film 32 composed of BST is formed by the sputteringmethod, the film is deposited with a RF power of 400 W and at asubstrate temperature of 300° C. and a gas pressure of 2.3 Pa and thencrystallized by heat treatment at 850° C. for about 30 minutes in anoxygen atmosphere to achieve a high dielectric constant. Similarly, theadhesive layer 20 and the dielectric barrier layer 41 may be formed bysputtering.

The capacitor portion 30 may have a structure including two dielectricthin films 32 or more, and each of the upper conductor 31 and the lowerconductor may have a multi-layer structure. Although, in thisembodiment, the upper conductor 31 and the lower conductor 33 arecomposed of Pt, a noble metal material can be used because it hasoxidation resistance in heat treatment at a high temperature when thedielectric thin film 32 is formed. Instead of Pt, for example, Ir, Ru,Au, or Pd can be used.

As the material used for the inorganic barrier layer 42, aluminum oxideor silicon oxide can be used instead of silicon nitride. However, inorder to improve the moisture resistance with a relatively small filmthickness, as in the embodiment, silicon nitride is preferably used.

Although, in the embodiment, BCB is used for the resin protective layer50, the material is not limited to this. A polyimide resin, an epoxyresin, or an acrylic resin can be used.

The thickness of each of the films described in the embodiment is onlyan example, and, of course, the thickness may be arbitrarily determinedwithin a range in which a thin film capacitor having low ESL can beobtained.

1. A thin film capacitor comprising: a substrate; a capacitor portionformed on the substrate and including a plurality of conductor layersand a dielectric film; a resin protective layer covering the capacitorportion; and a barrier layer interposed between the capacitor portionand the resin protective layer, the barrier layer including: acrystalline dielectric barrier layer formed in contact with thecapacitor portion and having a composition system the same as that ofthe dielectric thin film; and a non-conductive amorphous inorganicbarrier layer formed on a surface of the crystalline dielectric barrierlayer.
 2. The thin film capacitor according to claim 1, wherein thenon-conductive amorphous inorganic barrier layer contains at least onematerial selected from silicon nitride, aluminum oxide, and siliconoxide.
 3. The thin film capacitor according to claim 1, wherein thecrystalline dielectric barrier layer is composed of crystalline bariumstrontium titanate.
 4. The thin film capacitor according to claim 1,further comprising an adhesive layer provided between the substrate andthe capacitor portion.
 5. The thin film capacitor according to claim 4,wherein the adhesive layer has a composition system the same as that ofthe dielectric thin film.
 6. The thin film capacitor according to claim1, wherein the resin protective layer is composed of a material selectedfrom benzocyclobutene resin, polyimide resin, epoxy resin, and acrylicresin.
 7. A method of manufacturing a dielectric thin film capacitor,the method comprising: applying a first dielectric raw material solutioncontaining an organic metal compound on a substrate and heating thesolution to form an adhesive layer; alternately depositing, on theadhesive layer, a conductor layer and a dielectric thin film formed byapplying a second dielectric raw material solution with a compositionsystem the same as that of the first dielectric raw material solutionand heating the second solution to form a capacitor portion; applying,on the capacitor portion, a third dielectric raw material solution witha composition system the same as that of the first or second dielectricraw material solution and heating the third solution to form acrystalline dielectric barrier layer; heat treating at a temperature of750° C. or more in an oxygen atmosphere; forming a non-conductiveamorphous inorganic barrier layer on the dielectric barrier layer; andforming a resin protective layer on the inorganic barrier layer.